U.S. Pat. No. 4,589,301 discloses an adjustment device having a linearly continuously setable mechanism for the relative positioning of components. The device comprises a linearly displaceable spindle connected with a subject to be adjusted (for example the backrest of a seat). One end of the spindle is seated in a bore of a housing and an opposite end of the spindle is seated in a bore of a cup-shaped union nut which is in rotatable connection with the housing via a thread. A spindle nut is rotatably seated on the spindle in a chamber formed by the housing and the union nut. The device has recesses on its front end which respectively partially receive a roller bearing with axially acting spring elements. Axial forces of the spindle are smoothly supported via these bearings and the spindle nut can turn easily when the device is operated.
The device is locked by screwing the spindle nut onto the stationary housing part, reducing the axial play of the spindle nut until its annular front faces rest against the housing or are jammed. Once the spindle nut is fixed into place, the spindle can no longer be displaced and the device is locked.
This device is costly to produce and expensive to purchase due to the use of two relatively expensive roller body bearings for supporting the spindle nut. Also, long adjustment paths lead to space problems, because a spindle of appropriate length must be employed.
An automatic self-locking device for rotating shafts is disclosed in German Patent Publication DT 24 49 180 A1, which also permits the continuous quick adjustment of parts. A solitary helical spring, split into two spring parts, is seated with pre-stress on a cylindrical shaft. The spring has several stops which cooperate with corresponding stops of a housing surrounding the spring. A movement of the spring, and thus an adjustment of the adjustable part, is possible when the spring is opened. In the locked state, however, a load on the spring can result in an automatic increase of locking.
This device, too, has the disadvantage of a relatively elongated construction because of the two-part spring. In addition, the elastic behavior of the spring results in the selected locked position being resilient instead of rigid.
It is therefore desirable that a quick adjustment device be constructed that is manually operable, passive, and has a continuous action. It is desired that the quick adjustment device be adapted in particular for adjustable components in motor vehicles, which is distinguished by a great compactness, a simple structural design (easy mounting of few components) and dependable operation.